Studies On Method For Modal Parameter Identification And Damage Identification Of Engineering Structure

Modal parameter identification and damage identification technology ofengineering structures as a new subject to adapt to the actual needs of the project hasdeveloped for nearly20years, it has strong engineering background, also has importantpractical value. In recent years, the health monitoring and damage assessment ofengineering structure causes more and more attentions, modal parameter identificationand damage identification as its core technology and theoretical basis have becomeresearch hot spot in civil engineering field. It is too difficult to exert artificial excitationand efficiently measure excitation signal on engineering structures for their hugevolume, complex bind condition, mixed material, etc. Therefore traditional modalparameter identification theories and methods with testing input and output signal aredifficult to apply on engineering structures. Modal parameter identification underambient excitation have been widely used in the engineering field without applyingartificial incentives, without affecting the normal working, without measuring theexcitation signal, with low-cost and more in line with the actual situation, etc. theexisting modal parameter identification and damage identification methods have manydeficiencies in accuracy, robustness, efficiency and economic performance indicators,so they are still in the development stage, still need further study and perfect.To provide new technology and tools with scientific, quantitative, non-destructive,real-time for the existing engineering structure detection, identification and evaluation,in this paper we carry out deeply research for modal parameter identification methodsunder ambient excitation and damage identification method based on modal parametersensitivity, to sum up the main content as follow:①Through numerical analysis on a three layers framework model, we gotdisplacement response under ambient excitation, the two data pretreatment methods(random decrement technique and Next method) and five time domain modal parameteridentification method (ITD method, STD method, complex exponential method, ERAmethod and ARMA method) was selected to identify the modal parameters of thestructure, the results show: In the pretreatment methods Next method is superior torandom decrement technique method in terms of accuracy, anti-noise; STD method andARMA method are slightly higher than the other three methods in terms ofidentification accuracy, and STD method, ERA method ARMA method are slightly stronger than the other two methods in terms of anti-noise; frequency identificationaccuracy are much better than the damping identification accuracy in all methods.②Combined with the stochastic subspace method, we proposed three improvedmodal parameter identification methods under ambient excitation (improved ITDmethod, improved STD method, improved complex exponential method). Stochasticsubspace method has high identification accuracy, covariance of data can retain all theuseful information in the original data, simultaneously remove noise. The data inToeplitz matrix as input for the ITD method, STD method and complex index method,these three methods will no longer need random decrement technique or Next methodfor pre-processing, thereby eliminating the error caused by these two pretreatmentmethods. By identifying the modal parameters of a two spans three layers frameworkand a self-anchored suspension bridge, we could get the results: comparing thecorresponding stochastic subspace method, the accuracy of the improved methods basedon the covariance-driven SSI and data-driven SSI is not reduced, but have highercomputationally efficient, they only use less data can accurately identify the modalparameters of the system, and the recognition accuracy is high, noise resistance is better;comparing the ITD, STD, complex exponential method, the improving methods havethe advantage on the accuracy.③Modal identification experiments under ambient excitation on a frame structure,and modal parameter identification for the12-story reinforced concrete model shakingtable test were carried out in this paper. The recognition result further proved thecorrectness and feasibility of the proposed improved methods. In terms of accuracy ofthe five identification methods in the second chapter, ERA method is best, STD method,the complex exponential method and ARMA method closely followed, ITD method isthe worst. All methods can identify structural modal parameters under vibration effect.④In this paper, we researched denoising principle and component separationprinciple that based on singular value differential spectrum. The determination of modelorder method was proposed based on singular value differential spectrum for stochasticsubspace and ERA method. The model order by this method generats least false modal,and containes all useful modal, at the same time the recognition accuracy is not affectedand needs the smallest amount calculation. Through numerical analysis for theexperimental data, the modal identification results show that the method is effective.⑤To select real modal component and eliminate low frequency false modalcomponent, we applied correlation coefficient method. A digital filter to improve EMD decomposition was used, thereby overcoming the mode mixing phenomenon in EMDdecomposition. We proposed a denoising method based on singular value differentialspectrum for single-frequency components through EMD decomposition or digitalfiltering, simulated signals and experimental data analysis show that denoising effect ofthe method is quite obvious. We proposed a modal separation HHT method based onsingular value differential spectrum, through modal identification for simulated signalsand experimental data, it is proved that the method is feasible, also further broaden thehorizons for modal parameter identification under ambient excitation.⑥Improved three identification methods(STD method, complex exponentialmethod, ARMA method) were presented based on the digital filter, the analysis forsimulated signals and experimental data proved the correctness and feasibility of theimproved method, at the same time show that this method can effectively separate theintensive modal and without regard the problem that how to determine modal order inthe recognition process. We improved three identification methods (STD method,complex exponential method, ARMA method) based on EMD decomposition, theanalysis for simulated signals and experimental data proved the correctness andfeasibility of the improved method, at the same time show that this method caneffectively handle non-stationary signals and without regard the problem that how todetermine modal order.⑦Damage identification study based on improved modal parameter sensitivitymethod for a five-story frame structure has been done in this paper, we probed improveddirect analytical method for framework structural damage identification. Threeimprovements (including direct analytical method based on model reduction, theimprovement of modal truncation error, the improvement of the iterative solution of theequation) mainly be done. The numerical simulation analysis for the frame structureshow that: the recognition results is extremely correct in the case of noise-free, theresults suffer significant affect in the case of noise, but at the noise level of0.1%, for anacceptable recognition results guaranteed rate can reach80%or more. The research isuseful for scientific identification system in engineering structures, the developmentprovide a reference for the new test specifications.